netdev - Re: setsockopt()

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Message-ID: <20080709183432.GB5383@2ka.mipt.ru>
Date:	Wed, 9 Jul 2008 22:34:32 +0400
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Roland Dreier <rdreier@...co.com>
Cc:	Bill Fink <billfink@...dspring.com>,
	David Miller <davem@...emloft.net>, aglo@...i.umich.edu,
	shemminger@...tta.com, netdev@...r.kernel.org, rees@...ch.edu,
	bfields@...ldses.org
Subject: Re: setsockopt()

On Wed, Jul 09, 2008 at 11:10:31AM -0700, Roland Dreier (rdreier@...co.com) wrote:
> so somehow setting the window helps with the scheduling of
> processes... I guess autotuning lets some queue get too long or
> something like that.  The actual window doesn't matter too much, since
> the delay of the network is low enough that even though the bandwidth is
> very high, the BDP is quite small.  (With a 25 usec RTT, a 128 KB window
> should be enough for 40 Gbps, well over the raw link speed of 16 Gbps
> that I have)

That may be cache issues: depending on what application does it can be
useful or not to be bound to the same CPU. I suppose if benchmark looks
into the packet content, then it likely wants to be on the same CPU to
aliminate cache line ping-pongs, otherwise it only needs to be awakened
to send/receive next chunk, so having it on different CPU may result in
better its utilization...

-- 
	Evgeniy Polyakov
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